Vader didn't think outright dismantling her would get him what he wanted, necessarily. No, the dark-skinned Jedi Master was likely too mindful of where she was to let a petty thing like losing be enough to tip her over the edge.
Even if she had Fallen to the Dark Side, she still had all of her previous training to fall back on and enough self-awareness not to expose herself in the middle of the Jedi Temple. Never mind that Vader had already made sure to lock down this room in the Force, keeping anyone outside of it from sensing anything within.
Depa Billaba didn't know about that and he had no intention of just telling her either. No, this wasn't about revealing himself, this was about exposing her. In the face of overwhelming defeat, she would probably just accept the loss rather gracefully unless he went as far as to make her think he was actually trying to kill her.
Since he wasn't about to do that, Vader instead goes another route. He needs to take Depa's mind off of her mindfulness and distract her from her surroundings. While at the same time needling her to the point where she explodes. Luckily, Vader has… ideas.
He and Depa exchange a few more blows before he does it. Her Vaapad is as powerful as ever, though in the face of his amalgamation of a fighting style, it's not nearly good enough. Of course, Vader is fairly confident she doesn't realize that yet, not with how much he's holding back.
She's also not going to realize the disparity between them any time soon, not when she's about to be distracted by…
Their blades come together for a classic lightsaber lock and that's when Vader does it. Turning off his lightsaber, he watches as Depa's eyes widen and the Jedi Master starts to stumble forward. He steps past her own blade and reactivates his, scoring a light hit across Depa's midsection.
They're both using their lightsabers on lower settings for sparring, so the blow doesn't do much beyond startle her… but at the same time, the Jedi Master freezes completely, staring between him and her abdomen in disbelief for several long moments. Vader just steps back, blade at the ready.
"You... what was that, Skywalker?"
Lifting an eyebrow, Vader affects a look of pure innocence, hiding his smirk behind big, blue blinking eyes.
"What was what, Master Depa?"
Her eyes narrow at him as she looks for any hint of deceit. Funnily enough, she doesn't find it… which only confuses her more.
"Your lightsaber is malfunctioning. Again."
Vader holds in the urge to snort as she comes at him again and he once more moves to meet her. They fight for another few exchanges, about thirty seconds at most, before he does it again. Lightsaber goes off, Depa stumbles, lightsaber goes back on. This time, he scores a hit on her upper arm.
Also this time, Depa whirls on him, teeth bared in a momentary snarl.
"Stop that, Skywalker!"
Tilting his head to the side, Vader stops playing dumb.
"It's a viable tactic, Master."
Stiffening up as he admits to his 'crime', Depa frowns most severely.
"It is dishonorable."
Dishonorable. That word… is filled with so much bitterness and darkness that Vader thinks a lesser Sith might have choked on it. As it is, he feeds off of Depa's dark feelings easily. So that was what proceeded the Jedi Master's Fall. Honor and dishonor.
He could see it, he supposed. There was nothing honorable about the current state of the galaxy. Nothing honorable about the clone wars either. One could call it a sterile sort of war if one was being particularly obtuse or ignorant, but an honorable war? No shot.
When Vader doesn't offer a response, Depa's nostrils flare.
"You are a Jedi Knight, Skywalker. Act like it."
She comes at him a third time, clearly needing this fight more than she needs to lecture him. Vader meets her again, their blades clashing together. Of course, this time around, he can tell she's expecting it. Waiting for it even. The Dark Side flows through her all the more strongly as she tries to ride it's edge like a Vaapad User should, but more accurately wades through it like the Fallen Jedi she is.
Vader gives her a minute this time. Just long enough for her to get into her groove and think that she's getting the upper hand against him. And then, as she's starting to really get into the flow of things… he strikes once more. His lightsaber turns off, Depa tries to reorient clearly expecting it, but Vader is already moving around her, fluidly dodging her twitching saber as his own blade comes back on with a snap-hiss… and lightly lands across her buttocks.
The female Jedi Master's back arches, her lower body twitching forward against her will in a true display of broken composure. She also inhales sharply and the darkness within her roils with righteous fury and justified rage.
Vader waits to see what she will do next. How she will react. Will she snap or will she get control of herself and leave?
Finally, she turns to him, eyes blazing with suppressed anger as her nostrils flare. Vader, to be even more of a little shit, just shrugs.
"Honor isn't going to save us from the Separatists, Master Depa."
Vader can tell that his words land like a gut punch, even as Depa barely twitches outwardly. In the end, rather than let him draw her into that conversation…
"… Do not turn your lightsaber off again."
Oh, she shouldn't have been that specific. But then, Vader is honestly surprised she hasn't told him to leave just yet or stormed out in a huff herself. He knows just how annoying he's being right now, after all. For all that she's been doing some of her best bladework in this spar, she still hasn't landed a single blow on him. Meanwhile, he's struck her three times, all through using the same 'underhanded' tactic.
Still, she's put her foot down now. If he disobeys her, if he does the same thing a fourth time, then she will be well within her rights to not just end this spar but also punish and reprimand him for going against her orders. It's the perfect solution to handle her fraying self-control, at least in Depa's eyes.
There's just one problem… that specificity, as he'd mentioned earlier.
They meet in the middle of the room once more, sabers clashing in a shower of sparks as plasma beats against plasma. Vader can see Depa getting closer and closer to the point of no return. She's not even really on the edge like she probably thinks she is… no, she's already knee deep in the dark. Someone just needs to give her a proper push from behind and she'll face plant in her own Fallen Force Presence.
Luckily, Vader knows just the thing. And so, rather than turn HIS lightsaber off this time… he reaches out with the Force and flicks HERs off. The look on Depa Billaba's face is absolutely priceless as her saber sputters and dies on her. Vader's blade flicks out, scoring a light hit across her chest even as she's already rearing back.
He lets her retreat of course, even as he tilts his head to the side curiously.
"Master?"
Depa's eyes flick between her lightsaber and his face. He can tell exactly what she's thinking. She hadn't felt him reach out in the Force; Vader had made sure of that. But at the same time, what kind of coincidence would that be? For him to turn his saber off mid-combat three times, and then the fourth time it's hers that mysteriously 'fails'.
And yet… Vader isn't claiming credit. And while he's already shown her that he can lie to her with ease, he's not sure Depa completely understood that even when it was all but shoved in her face.
There's also the fact that technically, Vader shouldn't have been able to reach out and shut Depa's saber off like he'd been doing with his own. It was one of the earliest Force Techniques that the Jedi were taught. Your lightsaber was a part of you and once you built one, meditating with it and infusing it with your Force Presence was greatly encouraged.
As a result, stealing a Jedi's saber from their hands, or indeed interacting with it in any meaningful way… SHOULD be impossible. It would be easier to Force Grab the Jedi themselves rather than somehow messing with their weapon. That was how it was supposed to be, anyways. Vader cheated, like always.
Finally, the Jedi Master flicks her saber on and off as if to check it before shaking her head.
"… Let's continue."
She's close now. He can taste it in the air. Dominating her in a spar would have left her wallowing in her own inadequacies but annoying her like this is riling her up like nothing else. And the best part is, he's still winning. Four hits him, zero her.
They meet again, though this time Depa is more aggressive than ever before and, most interesting of all, no longer going for blade locks. Instead, she works a lot more dodges and deflections into her saber work. Not just that either, she's bringing kicks into things as well.
Ah… she's not using Vaapad anymore, at least not totally. At this point, Depa is dipping directly into Vaapad's predecessor, Juyo, the original Seventh Lightsaber Form.
Where Vaapad skirted the edge of the Dark Side and tended to use others' emotions against them while channeling your own darkness in a constructive manner, Juyo relied entirely on it's wielder's emotions and required complete mastery of said emotions to not Fall in the process of using it.
As a result, Juyo was all but banned in the modern Jedi Order… while Dark Side Practitioners like Maul and Ventress used it to great effect. The only true Master of Juyo that Vader had ever known though… was Darth Sidious.
Even now, Depa can't hold a candle to what Sidious was capable of with the emotion-fueled form. And at this point, she's barely hanging on by a thread.
Deciding to match her energy, Vader quits playing games. He snaps both their lightsabers off at the same time that Depa is throwing a kick in his direction. This allows him to step into the space where her blade was a moment before, grab her by the leg, and toss her across the room all too casually.
She flies through the air and slams into the wall with an explosion of breath from her lungs. Nothing too damaging, she'll just be one big bruise by tomorrow morning. But in the moment she hasn't even started feeling it. No, she's too busy feeling everything else.
"SKYWALKER!"
With that, it all boils over. Depa shrieks his name as she rises to her feet looking less like a Jedi Master and more like a mad woman. It reminds him a bit of Shaak Ti, but this is different. Where Shaak Ti had Fallen out of love and tried to kill him out of fear, Depa Billaba is pure rage right now. She's a roaring tempest in the Force, lashing out all around her.
The entire Jedi Order would be converging on their location at the moment if Vader wasn't containing things to just this private training room. But Depa is already too far gone to care, her eyes blazing a Dark Side Yellow as she flicks back on her lightsaber and takes a Force-Empowered leap across the room at him.
No more low settings. No more sparring. No, now Depa is truly trying to kill him. Tsk, tsk Master Jedi… how easily riled up you are.
Vader, of course, meets Depa's saber with his own. As tempting as it would be to bare his teeth at her and reveal his own Sith Eyes, he keeps his composure, a mask of perfect calm settled over his features as they fight to the death.
Or at least, Depa is fighting to the death anyways. Vader is still just playing around at this point, even if the stakes have been raised rather drastically. However, he's not holding back as much anymore. He's not hiding it at this point.
At first, the Jedi Master is too angry to notice. But the longer their bout goes on, the more and more Vader can see realization starting to dawn in Depa's blazing yellow eyes. She can't win. She never stood a chance of winning. He's much, much too strong for her. And frankly, he's the better duelist on top of his overwhelming power.
With that understanding comes the moment when Depa realizes what she's done as well. How she's lost control and let her true nature be exposed in the middle of the Jedi Temple. Vader sees her eyes flickering towards the door, no doubt expecting it to open at any moment and the likes of Windu and Yoda to come in and see her doing her best to kill the Chosen One while he handles her with unnatural calm.
When that doesn't happen though, he sees her getting more and more confused… before ultimately, that confusion gives in to despair. And with that despair comes… acceptance.
The moment Depa tries to turn her lightsaber on herself, Vader turns it off on her for a third time, stopping her from committing suicide. Then, he wrenches it from her grasp completely, tossing it across the room. It takes a second for the Fallen Jedi Master to realize what has happened… before she collapses to her knees, out of breath and panting.
All the fight goes out of her, even as she hangs her head before him.
"Kill me. Please."
Vader scoffs. Kill her? After all the work he put into making her confront her true nature? Fat chance of that happening…